a. Field of the Invention
The present invention relates generally to insulated windows, and, more particularly, to spacer frame tubing for spacing apart inner and outer panes of an insulated window, the tubing being constructed to accommodate inward and outward movement of the panes in response to changes in atmospheric pressure.
b. Related Art
It is well known in the art to provide insulated windows having more than one pane of glass, the panes being separated by an air space. Typically, the panes are maintained in spaced apart relationship by a frame that is interposed between their edges. The interior space between the panes, which is typically filled with air or other gas, thus serves as an insulator to reduce heat flow through the window. In the prior art it is known to manufacture the frame from a plurality of individual tubes joined at their ends to form a continuous frame, or of a single tube which is bent to form the frame. The tubes are generally made of aluminum alloy, or of molded plastic or other material having sufficient rigidity to maintain the space between the panes; aluminum alloy has the advantages of strength, stability and longevity for this use.
The tubing typically has a somewhat rectangular form so as to provide inner and outer side walls for supporting the glass panes, and the hollow interior of the tubing often contains a supply of desiccant material which removes moisture from the interpane air space. Examples of spacer tubes of this general configuration include those shown in U.S. Pat. Nos. 4,222,213 (Kessler), 4,576,841 (Limgemann), 5,439,716 (Larsen), and 5,581,971 (Peterson); many other examples of spacer frame tubing will occur to those skilled in the art.
Although very successful in most respects, it has been discovered that the configuration of conventional frame tubing may create a long term xe2x80x9cweak spotxe2x80x9d in many insulated window assemblies, especially those having relatively large, continuous panes of glass, such as are commonly used in office buildings and similar structures.
To illustrate this problem, FIG. 1 shows an example of conventional spacer frame tubing 10 installed between first and second glass panes 12, 14 so as to define the interpane air space 16. As was described above, the spacer tubing has a generally rectangular cross-section with first and second side walls 20, 22 for supporting the panes and a hollow interior 24 which is filled with granular desiccant material 26. In the version which is shown in FIGS. 1-3, the side walls are formed with raised ribs for minimizing the contact area with the glass panes, so as to minimize thermal transfer through the aluminum alloy material of the spacer. A strip of sealant material 28 is installed outside the spacer tubing, i.e., between the tube and the edges of the panes, so as to form an air tight seal which excludes the surrounding atmosphere and moisture from the interpane space 16. The sealant strip is normally formed of a polymeric material which has a degree of resilience and surface adhesion when new, but which tends to lose these qualities with age.
FIG. 1 shows the assembly in its initial configuration, with panes 12, 14 extending parallel to one another and resting more or less flat against the side walls of the spacer tubing and the surfaces of the sealant strip. As soon as the window is installed, however, the panes begin to undergo virtually continuous relative movement due to changes in atmospheric pressure. As was noted above, the window is hermetically sealed by the strip 28, so that the pressure in the interpane space does not equalize with that of the surrounding air. As a result, an increase in pressure, as is shown in FIG. 2, causes the two panes to bow inwardly, in the directions indicated by arrows 30a, 30b (this movement being somewhat exaggerated in the figures for purposes of illustration), with the greatest amount of inward deflection taking place towards the middle of the unsupported window and away from the spacer tubing 10. As this happens, the inner surfaces 32, 34 of the glass panes react and pivot against the side walls 20, 22 of the spacer tubing, with the result that the edge portions 36, 38 of the panes which extend beyond the spacer tubing move apart in corresponding, outward directions, as indicated by arrows 40a, 40b. This motion draws the inner surfaces 32, 34 of the panes outwardly, away from the surfaces 42, 44 of the sealant strip, with the result that the sealant eventually separates from the glass around the outer edges of the panes and thereby creates gaps and breaks in the seal, as indicated at arrows 46 and 48 in FIG. 2.
Conversely, a decrease in atmospheric pressure, as is illustrated in FIG. 3, causes the panes 12, 14 to bow outwardly towards their centers, as indicated by arrows 50a, 50b. As this happens, the sides 20, 22 of the spacer tubing again act somewhat in the manner of pivot points (due in part to the adhesion of the sealant material), and the edges 36, 38 of the panes press inwardly against the sealant strip 28 in the direction indicated by arrows 52a, 52b. This action tends to draw the inside surfaces of the panes away from the surfaces 42, 44 of the sealant along the sides of the spacer tubing, eventually causing the formation of additional gaps or openings, as indicated at 54, 56. Moreover, the sealant strip 28 resists being compressed between the edges of the glass panes, especially if the strip has hardened and lost it resilience, so much so that the edges of the panes can sometimes fracture and chip so as to leave little or no contact area between the pane and the sealant in the damaged area.
While the actual amounts of movement are comparatively small in absolute terms, they are significant (for example, the xe2x80x9cbellows effectxe2x80x9d generated by the flexing of the panes is sufficient to be employed to circulate the interpane air into and out of the desiccant material in some types of spacer tubing) and the resulting loads on the components can be quite great. In particular, with a very large window the distance from the unsupported centers of the panes to the spacer tubing around the perimeter of the window creates a very large lever arm as compared with the distance from the tubing to the outer edges of the panes, so that a small amount of movement at the centers of the panes results in comparatively large forces being exerted at the edges of the assembly.
The atmospheric pressure changes which generate these forces occur almost continuously, with pressures often fluctuating up and down several times in a single day, so that a window assembly may experience these forces/motions over several thousand cycles during its lifetime. As a result, the repeated pulling away from the sealant and/or chipping of the panes eventually leads to one or more breaches being formed in the hermetic seal around the edge of the window assembly. This allows moisture to enter the interpane space, so that the window quickly becomes fogged and must be replaced.
Many modern structures, such as large office towers are fitted with a huge number of insulated window assemblies. The cost of having to replace even a few of these window assemblies can be extraordinarily high, and so any improvement which extends the service life of the assemblies can easily translate to large economic savings.
Accordingly, there exists a need for a spacer tubing having a construction which reduces or eliminates the tendency of the outer edges of the glass panes in an insulated window assembly to pull away from and press against the sealant strip at the edge of the assembly as the panes flex inwardly and outwardly in response to changes in atmospheric pressure. Furthermore there exists a need for such a spacer tubing which has a hollow interior for containing a supply of desiccant material therein, and which permits a degree of fluid communication between the interior of the tubing and the interpane space so as to allow the desiccant material to withdraw moisture therefrom. Still further, there exists a need for such a spacer tubing which is economical to manufacture, and which is sufficiently strong and durable to enjoy a long service life. Still further, there exists a need for such a spacer tubing which is compatible with existing window assembly techniques, and which does not require special equipment or techniques in order to fabricate a spacer frame therefrom.
The present invention has solved the problems cited above. Broadly, this is a spacer frame tubing for being mounted between first and second glass panes in an insulated window assembly, the tubing comprising first and second side wall portions for engaging inner surfaces of the glass panes and a transverse wall portion interconnecting the side wall portions so as to support the side wall portions in spaced-apart relationship, the transverse wall portion being configured to permit the side wall portions to move alternately towards and away from one another in response to inward and outward forces inserted by the glass panes so as to minimize development of a pivoting action between the inside surfaces of the panes and the side wall portions of the tubing.
In a preferred embodiment, the transverse wall portion of the tubing may comprise at least first and second web portions which extend from the side wall portions and are joined by a seam structure, the seam structure being configured to permit the web portions to move alternately towards and away from one another in response to the inward and outward forces which are exerted by the glass panes in the window assembly. The seam structure may comprise a plurality of tab portions formed on edges of the first and second web portions, the tab portions on the first web portion forming a sliding interfit with the tab portions on the second web portion so as to permit the web portions to move alternately towards and away from one another without separating.
The tab portions on the edge of the first web portion may alternately overlap and underlap the tab portions on the edge of the second web portion in a sliding engagement therewith. The overlapping and underlapping tab portions may form generally planar engagement surfaces which extend generally parallel to the web portions, and the first and second web portions may extend in generally co-planar relationship to form a flat inner surface on the tubing.
The tab portions on each edge of the web portions may comprise alternating upper and lower tab portions, the upper tab portions extending in generally co-planar relationship with the web portions and the lower tab portions bending downwardly from base portions which are joined to the web portion. Each of the tab portions may comprise a substantially rectangular outer end, and the base portions of the lower tab portions may be positioned at spaced distances from the juxtapositioned outer ends of the upper tab portions so as to form gaps for permitting the ends of the upper tab portions to move towards the bases of the lower tab portions as the web portions move towards one another. The rectangular outer ends of the upper and lower tab portions may also comprise first and second edge faces for engaging the edge faces on adjoining tab portions in sliding interfit therewith.
The spacer frame tubing may further comprise a second transverse wall portion, so that the sidewall portions and transverse wall portions define a hollow interior of the tubing. The tubing may have generally rectangular cross section; and there may be at least one projecting rib formed on each side wall portion for limiting engagement with the inner surfaces of the glass panes to line-contact therewith; the projecting ribs may be formed proximate the transverse wall portion having the seam structure formed therein. A particulate desiccant material may be disposed within the hollow interior of the tubing.
The present invention also provides an insulated window assembly, comprising first and second glass panes having inner surfaces and spacer frame tubing mounted between the first and second glass panes, the tubing comprising first and second side wall portions for engaging inner surfaces of the glass panes and a transverse wall portion interconnecting the side wall portions so as to support the side wall portions in spaced apart relationship, the transverse wall portion being configured to permit the side wall portions to move alternately towards and away from one another in response to inward and outward forces exerted by the glass panes so as to minimize development of a pivoting action between the inner surfaces of the panes and the side wall portions of the tubing.
The spacer frame tubing may be mounted between outer edges of the glass panes proximate a perimeter of the window assembly, with said inward forces exerted against the sidewall portions of the tubing being caused by an inward bowing of the glass panes in response to an increase in atmospheric pressure, and the outward forces exerted against the sidewall portions of the tubing being caused by an outward bowing of the glass panes in response to a decrease in atmospheric pressure. The assembly may further comprise a sealant strip which is mounted between the outer edges of the glass panes outside of the spacer frame tubing.
These and other features and advantages of the present invention will be apparent from the reading of the following detailed description with reference to the associated figures.